This invention relates to a primer which is used as such in bonding, painting or printing and particularly, to a primer which is applied to non-polar or highly crystalline resins conventionally considered as difficult to bond, paint or print and which thus makes it possible to bond non-polar or highly crystalline resin substrates together or bond other material to the resin substrate, or paint or print on the surface of the resin substrate easily. The primer can be widely utilized in various fields, including automotive industries and electric appliance industries in which there have been widely utilized polyacetal resins and polyamide-imide resins called engineering plastics.
Non-polar or highly crystalline resins such as polyolefins typical of which are polyethylene, polypropylene, polybutene and polyfluoroethylene, polyethylene terephthalate, polyacetal, polyamide, polyvinylidene chloride, nylons and soft PVC films having large amounts of plasticizers, are materials which are difficult to bond, paint and print. These resin materials are not satisfactorily bonded together or painted or printed by the use of ordinary methods.
To improve these materials or resin substrates in adhesiveness, there has been heretofore proposed a surface treating method which comprises subjecting the substrates, for example, polyethylene or polypropylene, to flame treatment, corona discharge treatment, irradiation treatment or oxidizing treatment with a bichromate, sulfuric acid or the like so as to activate the surface of the substrate, that is, produce polar groups such as a carbonyl group in the surface of the substrates.
In addition, to make a resin such as polyfluoroethylene, which is impossible to oxidize on the surface, improved in adhesiveness, there have been proposed a special chemical treatment such as lithium vapor treatment, heat treatment with an alkali in a helium stream or treatment of metallic sodium with liquid ammonia and a satinizing process using a heat treatment in a solution of p-toluenesulfonic acid, a small amount of clay mineral and an organic solvent.
However, these treating methods need special equipments, are complicated to carry out, are unable to uniformly treat every part of the surface of a substrate having a complicated shape and require great expenses, these being disadvantageous.
Various primers also have been proposed. For example, Japanese Patent Appln. Laid-open Gazettes Nos. 52-98062, 56-141328 and 57-119929 have proposed primers prepared by dissolving a chlorinated polyethylene or chlorinated polypropylene or a fatty acid-modified acrylated alkyd resin in an organic solvent.
According to Japanese Pat. Appln. Laid-open Gazette No. 58-8734, however, the primers so proposed are unsatisfactory in adhesiveness to a paint although they are satisfactory in adhesiveness to a polyolefin substrate, or even if the paint and the polyolefin are satisfactory in adhesion to each other, the adhesiveness therebetween will undesirably decrease due to repetition of the cold/hot cycle.
If highly crystalline resins such as polyacetal resin and polyamide resin can be improved in adhesiveness or they can allow satisfactory coating, painting and printing on the surface thereof, they would be very beneficial to various fields such as automobile industry and electric appliance industry since they have many merits such as excellent physical properties, light weight, rust-proofness and low cost as a substitute for metallic materials.
In attempts to develop a surface treating method which is simple and speedy as compared with the conventional methods, the present inventors made intensive studies and, as a result of their studies, they developed desired primers which enable satisfactory adhesion, coating, painting and printing by using a composition comprising a certain kind of fluorine-containing compound and a specific type of compound as a primer for these purposes. The present invention is based on this development or finding.